It would be pretty useful for me to be able to have footnotes labelled by letter (a,b,c etc) rather than number (1,2,3 ...). That can reduce confusion with mathematical powers, or leaves superscripted numbers free to use, for example, as bibliographic references.

Would this be an easy thing to add to SimpleFootnotes, and would it be useful for other people? I imagine there are very few cases of >26 footnotes in a post, so running out of symbols is unlikely to be a problem (letters are also neater for footnotes 10-25, as only a single symbol is needed).